1. Technical Field
The disclosure relates to integrated circuit (IC) chip fabrication, and more particularly, to integrated circuits (IC) with resistors of lower topography and methods of forming a resistor below the first metal layer of a back-end-of-the-line (BEOL) interconnect structure.
2. Related Art
In the current state of the art, thin film resistors in integrated circuits are typically incorporated as part of the back-end-of-the-line (BEOL) interconnect. To establish connectivity between a device in the front-end-of-the-line (FEOL) to a thin film resistor in the BEOL, a wiring path traverses a myriad of connectivity points between many metal layers. The usual wiring path traverses a contact layer; a first metal layer; contacts that connect the metal layers; subsequent metal layers above the first metal layer; multiple thin film resistors; and, in reverse, to the first metal layer and then the contact layer. A simplified example of a typical integrated circuit 10 with such a wiring path is illustrated in FIG. 1. In this example, resistor 118 is connected to device 130 through contacts 116, first metal layer 114, second metal layer 110 and contacts in the BEOL 111, 112, hereinafter, BEOL contacts. The presence of thin film resistor 118 creates a variation in structure or topography which requires a contact formation process capable of forming two distinct types of BEOL contacts: BEOL contact 111, which contacts the resistor, and BEOL contact 112, which contacts the first metal layer. It is difficult to obtain a common process for these two types of BEOL contacts, especially if the height difference between BEOL contact 111 and BEOL contact 112 is large.
In view of the foregoing, it is desirable to configure thin film resistors which do not require formation of contacts of different heights or the creation of contacts of identical heights over varying topography created by the presence of the resistors.